Microsoft Excels @ insecurity

Guninski collars another bug

Microsoft has only partly fixed a flaw involving malicious script execution involving Office, according to veteran bug hunter Georgi Guninski.

Last week Microsoft issued a patch which meant users who use Word as an email editor in Outlook 2000 or 2002 could fall victim to script execution when a malicious memo is replied to or forwarded.

Outlook blocks scripts when an HTML email is viewed; but when Word is the editor, replying or forwarding calls it in an unprotected mode, and it then allows the script to run. The consequences of exploitation are running arbitrary code (potentially malware) on a local machine with the user's level of privilege.

Microsoft's patch fixes only the Outlook and Word issues and does not fix "at least the exploit path" through Excel, according to Guninski.

Guninski has published details of how it's possible to embed active content in an Excel (.XLS) file to create the same type of exploit created by the patched Outlook reply /forward bug.

The Veteran bug hunter published his Excel 'exploit' this morning without any input from Microsoft because of what he sees at the software giant's tardiness in responding to his concerns.

Although he has found holes in other platforms, Guninski has a particular penchant for uncovering various Microsoft vulnerabilities and has published their details before the software giant has come up with a patch. This has led to Microsoft branding him as "irresponsible" on more than one occasion in the past and strained relations between Redmond and the Bulgarian.

The original MS bulletin, along with links to its patch, can be found here.

Guninski's recommends that users consider disabling active scripting in IE as a workaround but suggests the best solution is for users to ditch MS client and Office applications. ®

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